Electronic devices containing active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes (OLEDs), organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices containing active organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.
An OLED device may comprise a substrate carrying an anode, a cathode and one or more organic light-emitting layers between the anode and cathode.
Holes are injected into the OLED device through the anode and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a light-emitting material present within the OLED device combine to form an exciton that releases its energy as light. In some devices a hole transporting layer is also provided, which functions to aid hole transport from the anode to the light emitting layer.
A light emitting layer may comprise a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton).
Phosphorescent dopants are also known (that is, a light-emitting dopant in which light is emitted via decay of a triplet exciton).
US2007/205714 discloses a copolymer comprising a repeat unit formed from a monomer having the following formula:

WO 2005/049546 discloses a polymer having the following structural units:

wherein each Ar is independently a substituted or unsubstituted aryl group; each Ar″ is a substituted or unsubstituted arylene group; and Z is a polycyclic arylene group.
It is an object of the invention to provide a hole-transporting polymer providing high efficiency whilst maintaining singlet and triplet energy levels which do not quench emission from the light emitting layer.